I voted for ORD as my top choice which is funny because it'd be my least favorite airport to travel through of those listed. I have never been to JFK so cannot comment on that. I'd probably rank them as follows:
1. ORD
2. LAX
3. MIA
4. DFW
You could probably flip LAX and MIA and I wouldn't argue much. I've been to LAX about a half dozen times and each of the others only once. My biggest reason for ranking these is based on layout. I've found most of the food, drinks, and showers as being for the most part similar among all of them. The layout in ORD is very nice and it was easy for me to find a secluded seat to not be bothered. I like the layout of DFW the least. I also didn't find the staff great at DFW and the last time I was there which was about 4 hours they weren't even doing any cook to order food (it was lunch time so maybe all don't). I've had excellent service at LAX both from agents when I needed help and the general staff.